Devices for testing writing instruments, in particular ballpoint pens, as known from the prior art, have the following structure: the device possesses a holder installed in such a way as to be able to pivot for a clamp which holds the ballpoint pen. The clamp is installed in the holder with a limited axial play and a small amount of radial play, usually 0.2 mm. Relative twisting is prevented by a dog.
During the test, the writing instrument is held at a predefined angle relative to the paper and optionally rotated about its longitudinal axis. The writing pressure is defined preferably by a weight.
The holder for the writing instrument (most of the time, several of these, preferably ten, are arranged one after the other) is installed in the test apparatus in such a way as to describe circular movements relative to the plane of the paper (10 to 90 rotations/minute are described in a circumference of 100 mm for example, which corresponds to writing speeds of 1 m/min to 9 m/min). The paper used to write on for test purposes is usually unwound from a reel and moved at a selectable speed underneath the holder, this being referred to as a forward movement. This produces a composite circular and linear movement, the forward movement being set small (preferably 0.17 [fine pattern] to 4.0 mm separation between each circle [coarse pattern]), in such a way that the divergence of the resulting circular shape is insignificant. To this composite movement there may be added, during the test operation, the movement of rotating the writing instrument about its own axis (preferably one rotation about its axis for every twenty circles with a fairly wide spacing between the circles, and one rotation about its axis for every one hundred circles in the case of a fine pattern).
The industry employs a number of different combinations of parameters of this type that make it a relatively simple process to observe, in the pattern obtained, the quality of the writing, particularly various anomalies, divergences and defects such as ovality, defective ink channels, in some circumstances defects of the writing ball, the suitability of the ballpoint pen ink used, etc., by observing a superposed interference pattern, the intensity of the lines or the intensity of the color.
The essential elements of this test method are standardized and described by the BSI in the documents PAS 40 (9.1.2) 1980 and DIN 16554 1982. The content of these two standards is incorporated in this application for reference.
The apparatus sold by Minitek Company under the name “PSU 10 Write Testing Machine” performs the above process. It has been used since 1962 by the major manufacturers and forms the technical basis for the standards. This apparatus and others using the same method test the production quality of some 100 million ballpoint pens every day around the world.
However, it has been found that this test, despite its usefulness, is not significant for all practical applications of writing instruments. In particular the regularity of the movement during the test does not coincide with the normal writing flow, because writing always includes making an abundance of spikes and angles and different accelerations. In addition, by its very nature, the test performed in accordance with the prior art results in superpositions of writing due to the superposition of the circular and forward movements. These superpositions of writing occur “wet on wet” because normal ballpoint pen inks can be smudged for up to about 20 seconds. These superpositions of writing complicate the evaluation of the test pattern, especially when using a densitometer with a small aperture.